What are the treads on the side of the highway called?

On the sides of most highways (in the U.S. at least), there are rough treads just outside the travel lanes to snap a driver to attention if the vehicle is drifting off the road. Is there a name for these things?

EDIT (post-answer for clarification, needed the answer to find the picture)
From the U.S. Department of Transportation's webpage:

Solution 1:

Those are called rumble strips.

Solution 2:

There's another variant here in Australia (and NZ, and I'm sure in other places too), which is a set of raised paint lines on the road which will give you a rumbling sound as you drive over them. The same technique is used in transition areas from high to low speed (like a highway exit) or where two lanes of high-speed traffic will be merging, that kinda thing where you want people to be awake.

A sample can be seen here, clearly showing the raised paint goop.

They're called, logically enough, 'audible lines', and are best defined as:

...a line on a road that is made up of a series of closely spaced raised pieces of material designed to create a continuous noise or vibration if driven on by a motor vehicle

(Reg 323A, New South Wales Road Rules 2008)